Double Talk Detector

1. A method of detecting that a received coded speech signal is dominated by a non-echo signal, comprising the steps of: if the signal power of a received speech signal exceeds a first threshold value, then extracting the Line Spectral Pairs (LSPs) from a coded speech frame of said received speech signal; converting each of said extracted LSPs into Line Spectral Frequencies (LSFs), ωi, and calculating the distance between each two adjacent LSFs; and, for each of said distances that is smaller than a second threshold value, calculating the frequency of the spectral peak, ωc, surrounded by said LSFs, and determining whether said spectral peak is an echo.

2. A method according to claim 1 , comprising the further steps of: incrementing a counter for each located spectral peak that is not an echo; indicating double-talk when the counter reaches a predetermined threshold value.

3. A method according to claim 1 , wherein the determination of whether a spectral peak is an echo comprises the steps of: extracting the LSPs from a coded speech frame of a first speech signal and converting said LSPs into the corresponding LSFs; and, determining that said spectral peak is an echo if the distance between the adjacent LSFs surrounding said spectral peak in the first speech signal is smaller than a third threshold value.

4. A method according to claim 1 , further comprising determining whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value.

5. A method according to claim 3 , further comprising searching for a closely located second spectral peak in the first speech signal if said spectral peak is not an echo, comprising the steps of: calculating a second spectral peak in the first speech signal from two adjacent LSFs; and, determining that said second spectral peak is an echo if the distance between the calculated second spectral peak and the centre frequency is smaller than a fifth threshold value.

6. A method according to claim 1 , wherein the LSFs are obtained by converting each of the extracted LSPs into the corresponding LSF using the relationship qi=cos(ωi).

7. A method according to claim 1 , wherein the centre frequency of a spectral peak is determined by locating two adjacent LSPs, ωi+1−ωi, and calculating ωc=(ωi+1−ωi)/2.

8. A method according to claim 2 , wherein, an indication of double talk deactivates an echo path estimation in a telecommunication system.

9. A method of estimating an echo path in a telecommunication system, wherein the echo path estimation is deactivated by a double talk indication obtained by a method according to claim 2 .

10. A method of estimating the echo path in a telecommunication system, wherein the echo path estimation is deactivated when a received coded speech signal is dominated by a non-echo-signal, the method comprising the steps of: if the signal power of a received speech signal exceeds a first threshold value, then extracting the Line Spectral Pairs (LSPs) from a coded speech frame of said received speech signal; converting each of said extracted LSPs into a corresponding Line Spectral Frequency (LSF), ωi, and calculating the distance between each two adjacent LSFs; for each distance that is smaller than a second threshold value, calculating the frequency of the spectral peak, ωc, surrounded by said LSF, and determining whether said spectral peak is an echo; and, deactivating the echo path estimation when a predetermined number of spectral non-echo peaks are located.

11. A method according to claim 10 , wherein the determination of whether a spectral peak is an echo comprises the steps of: extracting the LSPs from a coded speech frame of a first speech signal and converting each extracted LSP into the corresponding LSF; and, determining that said spectral peak is an echo if the distance between the LSFs surrounding said spectral peak in the first speech signal is smaller than a third threshold value.

12. A method according to claim 10 , further comprising determining whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value.

13. A method according to claim 10 , wherein the speech coding is based on AMR-CELP-coding.

14. A double talk detector arranged to be connected to a coded received speech signal and to a coded transmitted first speech signal in a telecommunication system for determining when said received speech signal is dominated by a non-echo signal, the double talk detector comprising: a signal power monitor arranged to determine when the signal power of a received speech signal exceeds a first threshold value; a spectral peak locator arranged to: extract the LSPs from a coded speech frame of the received speech signal and to convert each of said extracted LSPs into a corresponding LSF; and, calculate the distance between each two adjacent LSFs, and calculate a spectral peak, ωc, surrounded by two LSFs separated by a distance that is smaller than a second threshold value; and, an echo locator arranged to determine whether a located spectral peak is an echo.

15. A double talk detector according to claim 14 , further arranged to indicate that said received speech signal is dominated by a non-echo signal if a predetermined number of spectral non-echo peaks are located in the received signal.

16. A double talk detector according to claim 14 , further comprising a counter for counting the number of spectral non-echo peaks in the received speech signal.

17. A double talk detector according to claim 14 , wherein the echo locator is arranged to: extract the LSPs from a coded speech frame of the first speech signal and convert said extracted LSPs into the corresponding LSFs; and, calculate the distance between the adjacent LSFs surrounding said spectral peak and determine that the spectral peak is an echo if said calculated distance is smaller than a third threshold value.

18. A double talk detector according to claim 14 , wherein the echo locator is arranged to determine whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value.

19. A double talk detector according to claim 17 , wherein said echo locator is further arranged to search for a closely located second spectral peak in the first speech signal, if said spectral peak is not an echo, by: calculating a second spectral peak from said LSPs and determining that said second spectral peak is an echo if the distance to the centre frequency is smaller than a fifth threshold value.

20. A double talk detector according to claim 14 , wherein the LSFs are obtained by converting each of the extracted LSPs into the corresponding LSF using the relationship qi=cos(ωi).

21. A double talk detector according to claim 14 , wherein the centre frequency of a spectral peak is determined by locating two adjacent LSFs, ωi+1−ωi, and calculating ωc=(ωi+1−ωi)/2.

22. An echo path estimating device for a telecommunication system, arranged to deactivate the estimation of an echo path dominated by a non-echo-signal, comprising a double talk detector for a coded speech signal according to claim 14 .

23. An echo path estimating device for a telecommunication system, arranged to deactivate the estimation of an echo path dominated by a non-echo-signal, the echo path estimating device comprising: a double talk detector arranged to be connected to a coded received speech signal and to a coded transmitted first speech signal in said telecommunication system, said double talk detector comprising: a signal power monitor arranged to determine when the signal power of a received speech signal exceeds a first threshold value; a spectral peak locator arranged to: extract Line Spectral Pairs (LSPs) from a coded speech frame of the received speech signal and to convert each of said extracted LSPs into a corresponding Line Spectral Frequency (LSF), ωi; calculate the distance between each two adjacent LSFs, and calculate a spectral peak, ωc, surrounded by two LSFs separated by a distance that is smaller than a second threshold value; and, an echo locator arranged to determine whether a located spectral peak is an echo.

24. An echo path estimating device according to claim 23 , wherein the double talk detector is further arranged to indicate that said received speech signal is dominated by a non-echo signal if a predetermined number of spectral non-echo peaks are located in the received signal.

25. An echo path estimating device according to claim 24 , wherein the double talk detector comprises a counter for counting the number of spectral non-echo peak in the received signal.

26. An echo path estimating device according to claim 23 , wherein the echo locator is further arranged to: extract the LSPs from a coded speech frame of the first speech signal, and convert said extracted LSPs into the corresponding LSFs; and, calculate the distance between the adjacent LSFs surrounding said spectral peak and determine that the spectral peak is an echo if said calculated distance is smaller than a third threshold value.

27. An echo path estimating device according to claim 23 , wherein the echo locator is arranged to determine whether a spectral peak is an echo only if the frequency of said spectral peak is lower than a fourth threshold value.

28. An echo path estimating device according to claim 26 , wherein said echo locator is further arranged to search for a closely located second spectral peak in the first speech signal if said spectral peak is not an echo, by calculating a second spectral peak from two adjacent LSFs, and determining that said second spectral peak is an echo if the distance to the centre frequency is smaller than a fifth threshold value.